US5699490A - Method of and apparatus for generating correction table for image processing using the least square method - Google Patents
Method of and apparatus for generating correction table for image processing using the least square method Download PDFInfo
- Publication number
- US5699490A US5699490A US08/162,762 US16276293A US5699490A US 5699490 A US5699490 A US 5699490A US 16276293 A US16276293 A US 16276293A US 5699490 A US5699490 A US 5699490A
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- United States
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- data
- attribute
- correction table
- image
- halftone dot
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- 238000012937 correction Methods 0.000 title claims abstract description 43
- 238000000034 method Methods 0.000 title claims abstract description 27
- 238000012545 processing Methods 0.000 title claims description 17
- 230000001276 controlling effect Effects 0.000 description 9
- 230000006870 function Effects 0.000 description 8
- 238000010586 diagram Methods 0.000 description 7
- 230000000875 corresponding effect Effects 0.000 description 5
- 230000007246 mechanism Effects 0.000 description 5
- 230000000694 effects Effects 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- 230000004044 response Effects 0.000 description 3
- 238000003705 background correction Methods 0.000 description 2
- 230000002596 correlated effect Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000009966 trimming Methods 0.000 description 1
Images
Classifications
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T5/00—Image enhancement or restoration
- G06T5/90—Dynamic range modification of images or parts thereof
- G06T5/92—Dynamic range modification of images or parts thereof based on global image properties
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T5/00—Image enhancement or restoration
- G06T5/40—Image enhancement or restoration using histogram techniques
Definitions
- the present invention relates to a method of and an apparatus for producing a correction table for use in an image processing system.
- an image reading and reproducing system in which image information recorded on an original is electrically processed in an image processing device and outputted to an image output device for producing a master film.
- image data read from an original is processed for sharpness, gradation, color correction, and trimming, for example, and the processed image data is outputted to the image output device.
- An output signal with respect to the image density from the image processing device is quantized in 256 steps, for example.
- Such an image data signal is called as a quantum level data (referred to as "QL data").
- An image is reproduced in the image output device based on the QL data, and an exposure of the reproduced image is given to the film to produce a master film.
- an image having a halftone dot percentage different from that specified by the QL data other than a 50 halftone dot % image for example, corresponding to a value 128 of the QL data, can be reproduced depending on the output characteristics of the image output device.
- a correction table for adjusting the values of the QL data in advance is used so that a satisfactory image having a desired halftone dot percentage is reproduced by the image output device.
- a QL data having known various levels is first given to the image output device, and images reproduced from the QL data are exposed to the film so as to produce a test pattern, so-called a step-wedge. Then, the halftone dot percentage in the step-wedge is measured, and the measured halftone dot percentage data are correlated with the input QL data to know the input/output characteristics of the image output device.
- the measured input/output characteristics of the image output device can be used to produce the correction table which gives a required level of the input QL data to obtain an output image having a desired halftone dot percentage.
- An original QL data outputted from the image processing device is corrected by use of the correction table to a QL data which is actually given to the image output device and converted therein to an output image having a halftone dot percentage which is a high fidelity reproduction of the original QL data.
- the conventional processes are disadvantageous in that since the data are interpolated segmentwise over each of the data intervals, a local distortion may arise as shown in FIG. 6, if the halftone dot percentage data on the measured spots suffer an error.
- the resulted function formula may be such that does not pass through a prescribed starting point Pa (minimum value) and a prescribed ending point Pb (maximum value) as shown in FIG. 7.
- a correction table is produced based on such an approximation formula, a problem may arise that a precise expression of a shadow spot or a highlight spot in the reproduced image cannot be attained.
- a method of producing a correction table to be referred to when an input image data having a first attribute is converted into an image data having second attribute data which comprises steps of: measuring values of the first attribute data obtained by processing, with a given image output device, reference image data of the second attribute having a plurality of data values arranged at predetermined data intervals; determining an approximation formula of a desired function form for approximating the measured values of the first attribute data by the method of least squares, on the condition that the formula should pass through preset starting and ending points; and producing the correction table based on said approximation formula.
- the desired form of the approximation formula may be a polynomial of a prescribed degree
- the step of determining the approximation formula may comprise steps of: determining the maximum difference between the measured values and corresponding approximation values calculated according to the polynomial; incrementing the degree of the polynomial by 1, if the determined maximum difference exceeds a predetermined allowable range; repeating the step of determining the approximation formula until the maximum difference falls within the allowable range; and determining the polynomial with a degree at the time the maximum difference falls within the allowable range as being a resulted approximation formula.
- an apparatus for producing a correction table to be referred to when an input image data having a first attribute is converted into an image having second attribute data which comprises means for effecting every step of the method described in the above.
- an image having the first attribute data (e.g., halftone dot percentage) is produced and the data values are measured.
- An approximation formula is then determined by the method of least squares which approximates the measured values on the condition that the formula passes through a starting point (e.g., a shadow spot) and an ending point (e.g., a highlight spot).
- the correction table is produced based on the approximation formula determined in such a manner, the shadow and highlight spots in the reproduced image can be precisely expressed.
- a polynomial with a prescribed degree is solved as an approximation formula which passes through the starting and ending points, and the maximum difference is calculated between the first attribute data values and corresponding approximation values calculated according to the polynomial.
- the degree of the polynomial is repeatedly incremented by 1 until the maximum difference falls within a predetermined allowable range.
- a resultant approximation formula is determined as being the polynomial with a degree at the time the maximum difference falls within the allowable range.
- FIG. 1 is a diagram illustrative of a least square approximation according to the principles of the present invention
- FIG. 2 is a block diagram of a transmissive scanner in an image processing system which incorporates a method and an apparatus according to the present invention
- FIG. 3 is a block diagram of a reflective scanner in the image processing system which incorporates the method and the apparatus according to the present invention
- FIG. 4 is a block diagram of an image output device in the image processing system which incorporates the method and the apparatus according to the present invention
- FIG. 5 is a fragmentary diagram showing a produced step-wedge by way of example
- FIG. 6 is a diagram illustrative of interpolation of halftone dot percentage data and QL data according to a conventional process.
- FIG. 7 is a diagram illustrative of interpolation of halftone dot percentage data and QL data according to another conventional process.
- FIG. 2 shows an image reading, recording, and reproducing system 10 as an image processing system which incorporates a method and an apparatus according to the present invention.
- the image reading, recording, and reproducing system 10 generally comprises a transmissive scanner 12 for reading image information that is recorded on a transparent copy such as a reversal film, a reflective scanner 14 for reading image information that is recorded on a reflection copy such as a color photograph, an image output device 16 for reproducing and outputting, on a film, the image information that has been read by the transmissive scanner 12 or the reflective scanner 14, and a console unit 18 for controlling the transmissive scanner 12, the reflective scanner 14, and the image output device 16.
- a transmissive scanner 12 for reading image information that is recorded on a transparent copy such as a reversal film
- a reflective scanner 14 for reading image information that is recorded on a reflection copy such as a color photograph
- an image output device 16 for reproducing and outputting, on a film, the image information that has been read by the transmissive scanner 12 or the reflective
- the transmissive scanner 12 primarily comprises an image reader 20 for reading image information recorded on a transparent copy S T , a mechanism controller 22 for controlling operation of the mechanism of the transmissive scanner 12, and a central processing unit (CPU) 24 for controlling the transmissive scanner 12 in its entirety, calculations according to a function formula to generate a correction table, and the generation of such a correction table.
- the image reader 20 comprises a light source 26 for applying illuminating light to the transparent copy S T , a condensing lens 28 for converging the illuminating light that has passed through the transparent copy S T , and a charge-coupled device (CCD) unit 30 for converting the illuminating light falling thereon into electric image signals representing three primaries, R, G, B.
- the CCD unit 30 supplies the image signals to an analog-to-digital (A/D) converter 31, which converts the supplied image signals into digital image data.
- A/D analog-to-digital
- the mechanism controller 22 and the CPU 24 are connected to a system bus 32.
- a system bus 32 To the system bus 32, there are also connected a frame memory 34, a CCD compensator 36, an image pre-processor 38, a color processor 40, a magnification/sharpness adjuster 42, a correction table storage circuit 44, and a QL data generator 46 for generating QL data as pattern data.
- the frame memory 34 temporarily stores image information that is read by the image reader 20, and supplies the stored image information to a CRT display unit 48 of the console unit 18.
- the console unit 18 also has input ports including a mouse 50 and a keyboard 52.
- the CCD compensator 36, the image pre-processor 38, the color processor 40, the magnification/sharpness adjuster 42, the correction table storage circuit 44, and the QL data generator 46 perform functions, described below, under the control of the CPU 24.
- the CCD compensator 36 effects CCD dark-current correction and shading correction on the image data supplied from the A/D converter 31.
- the image pre-processor 38 converts output data from the CCD compensator 36 into density value data in the scanner, and also switches between the image data from the transmissive scanner 20 and the image data from the reflective scanner 14.
- the color processor 40 effects desired color processing on the image data outputted from the image pre-processor 38 based on image processing conditions.
- the magnification/sharpness adjuster 42 adjusts the magnification and sharpness of the image data outputted from the color processor 40.
- the correction table storage circuit 44 stores a table of QL data with respect to halftone dot percentage data. In response to the halftone dot percentage data outputted from the magnification/sharpness adjuster 42, the correction table storage circuit 44 reads and outputs QL data corresponding to the supplied halftone dot percentage data.
- the QL data generator 46 successively output QL data, e.g., QL data having values in 20 divisions of a range from 0 to 255, in response to an instruction.
- the CPU 24 functionally has a calculating means 24A and a write controlling means 24B. Responsive to halftone dot percentage data, from the keyboard 52, which are measured on an image produced by the image output device 16 that is supplied with reference image data at certain intervals from the QL data generator 46, the calculating means 24A calculates a curve in a least square approximation which passes through a starting point Pa and an ending point Pb that are determined in advance with respect to spots of the measured halftone dot percentage data. The write controlling means 24B produces image data with respect to the halftone dot percentage data based on the curve calculated by the calculating means 24A, and stores the produced image data in the correction table storage circuit 44.
- the calculating means 24A functionally has a first calculating means 24A 1 for solving a predefined polynomial as a polynomial with a predetermined degree on the condition that it passes through preset starting and ending points, a subtracting means 24A 2 for determining the difference between values of the measured halftone dot percentage data and corresponding values that are determined according to the polynomial with a predetermined degree solved by the first calculating means 24A 1 , and a repetitively instructing means 24A 3 for, if the difference falls out of a predetermined range, incrementing the degree of the polynomial by 1 and repetitively controlling the first calculating means 24A 1 and the subtracting means 24A 2 to effect calculations and subtractions until the difference falls in the predetermined range.
- FIG. 3 shows the reflective scanner 14 in block form.
- the reflective scanner 14 primarily comprises an image reader 56 for reading image information recorded on a reflection copy S R and a CPU 58 for controlling the reflective scanner 14 in its entirety.
- the image reader 56 comprises light sources 60 for applying illuminating light to the reflection copy S R , a plurality of reflecting mirrors 62 for directing, into a predetermined direction, illuminating light that is reflected by the reflection copy S R , a condensing lens 64 for converging the reflected illuminating light, and a CCD unit 66 for converting the illuminating light falling thereon into electric image signals representing three primaries, R, G, B.
- the CCD unit 66 supplies the image signals to an A/D converter 68, which converts the supplied image signals into digital image data.
- a CCD compensator 70 which is connected to the CPU 58 effects CCD dark-current correction and shading correction on the image data supplied from the A/D converter 68, and outputs the corrected image data to the image pre-processor 38 in the transmissive scanner 12.
- the image data read by the reflective scanner 14 is processed thereafter in the transmissive scanner 12 shown in FIG. 2.
- FIG. 4 shows the image output device 16 in block form.
- the image output device 16 primarily comprises a CPU 72 for controlling the image output device 16 in its entirety, a mechanism controller 74 for controlling operation of the mechanism of the image output device 16, and an image recorder 76 for recording image information on a film F.
- the CPU 72 is connected to a halftone dot generator 78 which generates a halftone dot signal from the image data supplied from the correction table storage circuit 44 or the QL data generator 46 in the transmissive scanner 12.
- the generated halftone dot signal is supplied to a laser diode (LD) driver 80.
- the LD driver 80 energizes a laser diode 82 in the image recorder 76 based on the supplied halftone dot signal.
- LD laser diode
- the image recorder 76 comprises, in addition to the laser diode 82, a light deflector 84 for deflecting and scanning a laser beam L in a main scanning direction, and a condensing lens 86 for converging the deflected laser beam L onto the film F.
- QL data are generated in a successively increasing order, e.g., 21 QL data of "0", “13", “26”, “38”, . . . , are successively generated, by the QL data generator 46, and outputted to the image output device 16.
- the halftone dot generator 78 In response to the supplied QL data, the halftone dot generator 78 generates halftone dot data under the control of the CPU 72, and outputs the generated halftone dot data to enable the LD driver 80 to energize the laser diode 82.
- the laser diode 82 emits a laser beam L based on the halftone dot data.
- the emitted laser beam L is deflected by the light deflector 84 and converged by the condensing lens 86 onto the film F, thereby forming a step-wedge on the film F.
- FIG. 5 shows such a formed step-wedge by way of example.
- the halftone dot percentage data of respective steps of the step-wedge which is generated in the correction table generating routine are read by a separate measuring unit.
- the measured halftone dot percentage data are then inputted into the frame memory 34 through the keyboard 52 in the order of magnitude of the QL data, e.g., from the left of the step-wedge.
- the measured halftone dot percentage data are inputted, they correspond to the QL data that are outputted by the image output device 16, as indicated by spots x plotted in FIG. 1.
- the halftone dot percentage data vs. QL data shown in FIG. 1 are approximated in a least square approximation by an m-th order polynomial, on the condition that it passes through a starting point Pa (minimum value) and an ending point Pb (maximum value), as follows:
- a correction table is generated according to the function equation.
- the degree m will be described below.
- the curve based on a polynomial with a degree at the time ⁇ i ⁇ is as indicated by a, for example, in FIG. 1.
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Theoretical Computer Science (AREA)
- Facsimile Image Signal Circuits (AREA)
- Image Processing (AREA)
- Image Input (AREA)
Abstract
Description
y=c.sub.0 +c.sub.1 x
c.sub.0 =(x.sub.b y.sub.a -x.sub.a y.sub.b)/(x.sub.b -x.sub.a)
c.sub.1 =(y.sub.b -y.sub.a)/(x.sub.b -x.sub.a). (3)
δ.sub.i =|y.sub.i -(c.sub.o +c.sub.1 x.sub.i)|≦δ (14)
δ.sub.i =|y.sub.i -(c.sub.o +c.sub.1 x.sub.i)|>δ (15)
y=c.sub.0 -c.sub.1 x+c.sub.2 x.sup.2. (16)
Claims (12)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP00679693A JP3478553B2 (en) | 1993-01-19 | 1993-01-19 | Correction table generation method and apparatus |
JP5-6796 | 1993-01-19 |
Publications (1)
Publication Number | Publication Date |
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US5699490A true US5699490A (en) | 1997-12-16 |
Family
ID=11648145
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US08/162,762 Expired - Fee Related US5699490A (en) | 1993-01-19 | 1993-12-07 | Method of and apparatus for generating correction table for image processing using the least square method |
Country Status (4)
Country | Link |
---|---|
US (1) | US5699490A (en) |
EP (1) | EP0609567B1 (en) |
JP (1) | JP3478553B2 (en) |
DE (1) | DE69330384T2 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6141114A (en) * | 1998-01-08 | 2000-10-31 | Xerox Corporation | Edge enhanced error diffusion with artifact correction in areas of highlights and shadows |
CN1317604C (en) * | 2004-12-20 | 2007-05-23 | 北京北大方正电子有限公司 | Generating method of linear circular shaped lattice point for printing machine |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE69900270T2 (en) * | 1998-04-03 | 2002-07-25 | Da Vinci Systems, Inc. | Device for generating adapted gamma curves for a color correction system |
DE69900872D1 (en) | 1998-04-03 | 2002-03-21 | Da Vinci Systems Inc | Primary and secondary color processing using color, saturation, luminance and surface insulation |
US6469747B1 (en) | 1999-09-02 | 2002-10-22 | Da Vinco Systems, Inc. | Parabolic mixer for video signals |
KR100710258B1 (en) * | 2005-06-01 | 2007-04-20 | 엘지전자 주식회사 | Apparatus and method for regulating tone of video signal in a display device |
Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
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US4841362A (en) * | 1983-07-04 | 1989-06-20 | Fuji Photo Film Co., Ltd. | Apparatus for generating positive or negative image output signals from either positive or negative originals |
US5103298A (en) * | 1989-09-19 | 1992-04-07 | Ikegami Tsushinki Co., Ltd. | Error correction method and circuit for nonlinear quantization circuit |
US5175621A (en) * | 1989-08-10 | 1992-12-29 | Ikegami Tsushinki Co., Ltd. | Gamma correction circuit and method thereof |
US5309526A (en) * | 1989-05-04 | 1994-05-03 | At&T Bell Laboratories | Image processing system |
US5311332A (en) * | 1990-12-20 | 1994-05-10 | Ricoh Company, Ltd. | Interpolation method and color correction method using interpolation |
US5373567A (en) * | 1992-01-13 | 1994-12-13 | Nikon Corporation | Method and apparatus for pattern matching |
Family Cites Families (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5179528A (en) * | 1989-11-22 | 1993-01-12 | Texas Instruments Incorporated | Signal processing system and method implementing a non-linear transfer function approximated by a piecewise linear transformation |
-
1993
- 1993-01-19 JP JP00679693A patent/JP3478553B2/en not_active Expired - Fee Related
- 1993-12-07 US US08/162,762 patent/US5699490A/en not_active Expired - Fee Related
- 1993-12-29 DE DE69330384T patent/DE69330384T2/en not_active Expired - Fee Related
- 1993-12-29 EP EP93121079A patent/EP0609567B1/en not_active Expired - Lifetime
Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4841362A (en) * | 1983-07-04 | 1989-06-20 | Fuji Photo Film Co., Ltd. | Apparatus for generating positive or negative image output signals from either positive or negative originals |
US5309526A (en) * | 1989-05-04 | 1994-05-03 | At&T Bell Laboratories | Image processing system |
US5175621A (en) * | 1989-08-10 | 1992-12-29 | Ikegami Tsushinki Co., Ltd. | Gamma correction circuit and method thereof |
US5103298A (en) * | 1989-09-19 | 1992-04-07 | Ikegami Tsushinki Co., Ltd. | Error correction method and circuit for nonlinear quantization circuit |
US5311332A (en) * | 1990-12-20 | 1994-05-10 | Ricoh Company, Ltd. | Interpolation method and color correction method using interpolation |
US5373567A (en) * | 1992-01-13 | 1994-12-13 | Nikon Corporation | Method and apparatus for pattern matching |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6141114A (en) * | 1998-01-08 | 2000-10-31 | Xerox Corporation | Edge enhanced error diffusion with artifact correction in areas of highlights and shadows |
CN1317604C (en) * | 2004-12-20 | 2007-05-23 | 北京北大方正电子有限公司 | Generating method of linear circular shaped lattice point for printing machine |
Also Published As
Publication number | Publication date |
---|---|
EP0609567B1 (en) | 2001-06-27 |
DE69330384T2 (en) | 2001-10-11 |
JP3478553B2 (en) | 2003-12-15 |
JPH06217142A (en) | 1994-08-05 |
EP0609567A2 (en) | 1994-08-10 |
EP0609567A3 (en) | 1994-10-12 |
DE69330384D1 (en) | 2001-08-02 |
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